1. Field of the Invention
The present invention relates generally to oil and gas well completion and remedial methods, and more particularly, to well completion and remedial methods utilizing compositions consisting essentially of rubber latex and hydraulic cement.
2. Description of the Prior Art
A variety of oil and gas well completion and remedial methods have heretofore involved the use of hydraulic cement compositions. Such cement compositions have been and are usually comprised of a water slurry of Portland cement together with various additives such as set time accelerators, retarders, fluid loss reducers, dispersants, and the like. The cement slurries are pumped into completion or remedial locations within well bores and/or subterranean formations penetrated thereby and allowed to set into hard impermeable masses.
A principal well completion technique which utilizes a cement composition is known as primary well cementing. Primary well cementing involves placing a cement composition into the annulus between the walls of the well bore and a conduit, e.g., casing, disposed therein, and allowing the cement composition to set therein, whereby the exterior surfaces of the conduit are bonded to the walls of the well bore. The bonding of the conduit within the well bore serves to maintain the conduit in place and to prevent formation fluids from communicating between subterranean formations or zones or to the surface by way of the annulus.
Primary cementing operations utilizing hydraulic cement compositions have generally been very successful, however, when primary cementing is carried out in wells wherein high temperatures and/or high pressures are exerted on the casing or liners cemented therein, failure of the cement seal can occur with the result that pressurized fluids from subterranean formations or zones are allowed to flow therebetween or to the surface by way of the annulus. The failure of the primary cement in a well bore can bring about lost revenues as a result of lost production, and, because of escaping hydrocarbons, can create a highly dangerous well condition.
Failure of the primary cement sheath in a well bore can be due to the exposure of the metal conduit contacted by the cement in the well bore to high temperature as a result of hot fluids being produced from the well and/or to the exposure of the metal conduit to high internal test pressures or treatment fluid pressures. Such high temperature and pressure differentials cause the conduit to expand both diametrically and circumferentially which causes failure of the bond at the cement-casing interface and/or causes the cement sheath to fracture radially from the inner casing surface to the outer well bore wall.
In other well completion or remedial operations which utilize hydraulic cement compositions, e.g., secondary squeeze cementing and other similar operations wherein cracks, voids and other areas are filled with cement and sealed and/or whereby temporary or permanent cement plugs are formed in the well, desired results are often not achieved because the set cement lacks resilience, high tensile strength or acid and other chemical resistance. Thus, there is a need for an improved pumpable composition which will set into a hard impermeable mass for use in well completion and remedial methods which provides improved elasticity, resilience, tensile strength, chemical resistance and low permeability.